The ARM system handles setting all power and channel setting, including moving the APs to new channel and power settings automatically when appropriate. The network administrator spends no time managing the RF environment even in the case of RF jamming attacks or interference from legitimate wireless sources in the same frequency. The system automatically determines the best settings, and can automatically move away from interference laden channels without any intervention. The ARM system works indoors or outdoors.
Sometimes a channel change is desirable but to do so would interrupt active user sessions. Certain types of devices are more tolerant of such changes than others. Because the Mobility Controller is aware of not only users on the AP but also the type of traffic being sent, the AP can be directed not to change channels for specific client types. It can be set to pause scanning if going off channel will cause unacceptable quality disruption. These features are called Client Aware and Voice Aware Scanning.
Aruba Client Aware Scanning prevents a channel change while clients are associated with a particular AP. This ensures that clients will continue to send and receive data without the AP suddenly switching to a new channel. When all clients have left a particular AP, it is free to change channels. While the client is attached, it will continue to go off channel for scanning at predetermined intervals unless ARM scanning is disabled.
If the customer has chosen not to deploy dedicated Air Monitors, the system can still obtain the information it needs to conduct basic WIPS and ARM functions by ‘timesharing’ with the data traffic on each AP. This scanning is transparent to data users, but can have detrimental effects on isochronous traffic flows such as voice calls. With Aruba Voice Aware Scanning, in the optional Voice Services Module, the AP will temporarily stop channel scanning when calls are in progress. Because the Mobility Controller is aware of the state of the call, it will pause scanning when the phone goes “off hook” and resume scanning when the call ends.
ARM is typically run in a very aggressive mode when the network is first deployed, allowing the APs to quickly settle their power and channel settings. The following setting should be used to initially settle the network infrastructure, and should be configured in a new profile:
Parameter | Value | |
Assignment | ||
Client Aware | Disabled | |
Max Tx Power | 30 | dBm |
Min Tx Power | 11 | dBm |
Multi Band Scan | Disabled | |
Rogue AP Aware | Disabled | |
Scan Interval | 1 sec | |
Scanning | Enabled | |
Scan Time | 110 msec | |
Power Save Aware Scan | Disabled | |
Ideal Coverage Index | 5 |
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Acceptable Coverage Index | 2 |
|
Wait Time | 2 sec | |
Free Channel Index | 25 |
|
Backoff Time | 120 sec | |
Error Rate Threshold | 50 | % |
Error Rate Wait Time | 30 | sec |
Noise Threshold | 75 | |
Noise Wait Time | 120 sec | |
Minimum Scan Time | 2 sec | |
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Campus Wireless Networks Validated Reference Design Version 3.3 Design Guide | RF Planning and Operation 57 |
